Persistent activation of phosphatidylinositol 3-kinase causes insulin resistance due to accelerated insulin-induced insulin receptor substrate-1 degradation in 3T3-L1 adipocytes
Persistent activation of phosphatidylinositol 3-kinase causes insulin resistance due to accelerated insulin-induced insulin receptor substrate-1 degradation in 3T3-L1 adipocytes
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DOI：
10.1210/en.141.6.1930
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发表时间：
2000-06-01
期刊：
影响因子：
4.8
通讯作者：
Olefsky, JM
中科院分区：
文献类型：
--
作者：
Egawa, K;Nakashima, N;Olefsky, JM
最近，我们报道了膜靶向磷脂酰肌醇(PI)3-激酶(P110CAAX)的过表达在无胰岛素的情况下促进了3T3-L1脂肪细胞的p70S6激酶、Akt、葡萄糖转运和RAS的激活，但抑制了胰岛素刺激的糖原合成酶的激活和MAP激酶的磷酸化。为了探讨p110CAAX诱导细胞胰岛素抵抗的机制，我们研究了p110CAAX对胰岛素受体底物(IRS)-1蛋白的影响。P110CAAX单独过表达使IRS-1蛋白水平降低至对照组的63+/-10%。胰岛素治疗导致IRS-1凝胶迁移率改变(最可能由丝氨酸/苏氨酸磷酸化引起)，随后IRS-1降解。此外，p110CAAX的表达增强了胰岛素诱导的IRS-1的降解(在20min时为61+/-16%，而在20min时为13+/-15%，在80+/-8us时为+/-8%)。胰岛素刺激60min时p110CAAX表达或不表达分别为41+/-12%)。在p110CAAX表达的细胞中，胰岛素刺激的IRS-1与PI3K的P85亚单位之间的结合也降低了，尽管PI S激酶的总活性增加，但IRS-1相关的PI3K活性却降低了。Wortmannin处理5h可抑制丝氨酸/苏氨酸的磷酸化和IRS-1蛋白的降解。这些结果表明，胰岛素治疗导致IRS-1丝氨酸/苏氨酸磷酸化，随后IRS-1降解，这是通过PI 3-激酶敏感的机制实现的。与此一致，活化的PI 3-激酶使丝氨酸/苏氨酸残基上的IRS-1磷酸化，导致IRS-1降解。IRS-2和IRS-1也观察到了类似的发现。这些结果也可能解释了慢性p110CAAX表达导致的细胞胰岛素抵抗状态。
Recently, we have reported that the overexpression of a membrane-targeted phosphatidylinositol (PI) 3-kinase (p110CAAX) stimulated p70S6 kinase, Akt, glucose transport, and Ras activation in the absence of insulin but inhibited insulin-stimulated glycogen synthase activation and MAP kinase phosphorylation in 3T3-L1 adipocytes. To investigate the mechanism of p110CAAX-induced cellular insulin resistance, we have now studied the effect of p110CAAX on insulin receptor substrate (IRS)-1 protein. Overexpression of p110CAAX alone decreased IRS-1 protein levels to 63 +/- 10% of control values. Insulin treatment led to an IRS-1 gel mobility shift (most likely caused by serine/threonine phosphorylation), with subsequent IRS-1 degradation. Moreover, insulin-induced IRS-1 degradation was enhanced by expression of p110CAAX (61 +/- 16% vs. 13 +/- 15% at 20 min, and 80 +/- 8% us. 41 +/- 12% at 60 min, after insulin stimulation with or without p110CAAX expression, respectively). In accordance with the decreased IRS-1 protein, the insulin-stimulated association between IRS-1 and the p85 subunit of PI 3-kinase was also decreased in the p110CAAX-expressing cells, and IRS-1-associated PI 3-kinase activity was decreased despite the fact that total PI S-kinase activity was increased. Five hours of wortmannin pretreatment inhibited both serine/threonine phosphorylation and degradation of IRS-1 protein. These results indicate that insulin treatment leads to serine/threonine phosphorylation of IRS-1, with subsequent IRS-1 degradation, through a PI 3-kinase-sensitive mechanism. Consistent with this, activated PI 3-kinase phosphorylates IRS-1 on serine/threonine residues, leading to IRS-1 degradation. The similar finding was observed in IRS-2 as well as IRS-1. These results may also explain the cellular insulin-resistant state induced by chronic p110CAAX expression.